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'''Quantum mechanics''' (QM) is the branch of [[physics]] that describes the behavior of systems on very small length and energy scales, such as those found in the structure and interaction of [[atom]]ic and subatomic particles.<ref>The quantum in QM is [[Planck's constant]]. Its units are angular (or rotational) momentum. If the value of this constant were much, much larger, then a human being might be able to perceive the impact of the constant by twirling around and feeling the jumps (or quantum leaps) in the rotational momentum of their body (and thus the perceivable rotational speed) as their body jumped from one multiple of the constant to another. There are many non-intuitive implications of such a quantization. Perhaps the most immediate implication of the constant is the discrete nature of the first electron orbital of the hydrogen atom. As one proceeds to higher orbitals, non-intuitive non-spherical three-dimensional harmonic patterns emerge and these dominate in the next-higher-level structure of matter. An important example for humans is p-orbitals of the carbon atom that implement the carbon chains of the macromolecules that implement all known forms of life. There are many other non-intuitive implications of QM. QM has gone through several distinct mathematical formulations. The implications of QM that are well-understood are considered by most scientists to be laws of nature.</ref>

'''Quantum mechanics''' (QM) is the branch of [[physics]] that describes the behavior of systems on very small length and energy scales, such as those found in the structure and interaction of [[atom]]ic and subatomic particles.<ref>The quantum in QM is [[Planck's constant]]. Its units are angular (or rotational) momentum. If the value of this constant were much, much larger, then a human being might be able to perceive the impact of the constant by pulling the string to spin up a very rigid toy gyroscope. They would feel tugs at the gyro acquired more units of the constant. They could then set the gyro down in its frame and watch the rate of spin reduce due to friction in steps, rather than smoothly, and then finally abruptly snap down to a resting state. There are many non-intuitive implications of such a quantization. Perhaps the most immediate implication of the constant is the discrete nature of the first electron orbital of the hydrogen atom. As one proceeds to higher orbitals, non-intuitive non-spherical three-dimensional harmonic patterns emerge and these dominate in the next-higher-level structure of matter. An important example for humans is p-orbitals of the carbon atom that implement the carbon chains of the macromolecules that implement all known forms of life. There are many other non-intuitive implications of QM. QM has gone through several distinct mathematical formulations. The implications of QM that are well-understood are considered by most scientists to be laws of nature.</ref>

A fundamental principle of quantum mechanics is that there is an uncertainty in the location of a subatomic particle until attention is focused on it by observing its location.  This insight is essential for understanding certain concepts that [[classical physics]] cannot explain, such as the discrete nature of small-scale interactions, [[wave-particle duality]], the [[uncertainty principle]], and [[quantum entanglement]].  Quantum mechanics forms the basis for our understanding of many phenomena, including [[chemical reaction]]s and [[radioactive decay]], and is used by all [[computer]]s and electronic devices today.  In addition, quantum mechanics explains why the [[Second Law of Thermodynamics]] is always true.

A fundamental principle of quantum mechanics is that there is an uncertainty in the location of a subatomic particle until attention is focused on it by observing its location.  This insight is essential for understanding certain concepts that [[classical physics]] cannot explain, such as the discrete nature of small-scale interactions, [[wave-particle duality]], the [[uncertainty principle]], and [[quantum entanglement]].  Quantum mechanics forms the basis for our understanding of many phenomena, including [[chemical reaction]]s and [[radioactive decay]], and is used by all [[computer]]s and electronic devices today.  In addition, quantum mechanics explains why the [[Second Law of Thermodynamics]] is always true.